This invention relates to a method of separately counting the respective numbers of particles of plural kinds included in the same specimen and, for example, to a so-called blood cell counting method for seeking the numbers of lymphocytes, monocytes and granulocytes in white blood cells.
Such prior art blood cell counting has been effected as follows, as disclosed, for example, in the U.S. Pat. No. 4,661,913. Blood extracted from a human body is first subjected to a predetermined preliminary treatment to provide a specimen and it is supplied to a suitable particle detector to measure two kinds of properties of each blood cell. Then, a suitable XY co-ordinate system is established and the blood cell is plotted on the co-ordinate system using two kinds of measured values thereof as its X and Y coordinates, respectively. All blood cells in the specimen are plotted in the same manner to produce a distribution diagram so-called "scattergram" of the particles regarding both properties as above-mentioned. Thereafter, boundaries for partitioning clusters of the respective blood cells, namely, lymphocytes, monocytes and granulocytes are drafted on the scattergram and the number of plots within each boundary is then counted.
In this method, it is easy to define the boundaries and highly accurate count values are obtainable when the clusters of the respective kinds of blood cells are clearly separated from each other on the scattergram. When the respective clusters are mutually close or overlapping as in conventional scattergrams, however, it is difficult to define the boundaries uniquely without use of any auxiliary knowledge and information and the counting accuracy is reduced since the count of each kind of blood cells varies with the mode of selection of the boundary. Moreover, the auxiliary knowledge and information are obtained experimentally in accordance with the kind of particles and have no universality in use and a lot of labor and time are needed for prepartion thereof.
In order to remove this problem, a fuzzy clustering method in which any plot unclearly belonging to a specific cluster is assigned partially to two or more clusters has been proposed. Although this method is suitable for analyzing the distribution since fuzziness can be expressed naturally, it has such a problem in that a very long operation time due to complicated algorithm is needed and, for example, even a personal computer having a thirty-two bit central processing unit may need a time as long as one minute or more.